The present invention relates to a method for bending and tempering a glass sheet, in which method a glass sheet supported by a ring mould is heated to a softening temperature, the glass sheet is allowed to bend gravitationally and the bent glass sheet is advanced to tempering.
The invention relates also to an apparatus for bending and tempering a glass sheet, said apparatus comprising a ring mould for supporting a glass sheet at various stages of handling, a preheating station, and a quenching station.
The invention is particularly well suited for bending relatively simple glass shapes which can be bent gravitationally by using a ring mould. Most of the automotive side windows and backlights are such simple shapes or forms that can be bent by using a method and apparatus of the invention. For essentially the same purpose there is a prior known method, wherein a piece of homothermal glass is dropped onto a ring mould and the piece of glass assumes its proper form by virtue of inertial force and the shape of a ring mould. This prior known method offers the advantages of high capacity and reliability but its drawbacks include a high price, a rather long form replacement time (4-5 h), marks caused by dropping on the glass border areas, and the high price of tools required by individual pieces of glass.
On the other hand, there are known single furnaces operating on the ring mould principle, wherein the glass is only heated from above and the glass bends to its shape or form whose bending depth is determined by adjusting the heating time. An advantage offered by single furnace is a simple construction and a low price but there are also drawbacks, including a low capacity, a relatively high minimum thickness (typically 5 mm, sometimes 4 mm), simple bending shapes and fairly good bending accuracy (as the bending depth is only controlled by means of heating time).
An object of the invention is to provide an improved method and apparatus, capable of offering the following benefits:
economical price in view of capacity;
a reachable glass thickness is substantially below 4 mm, typically a 3,2 mm minimum thickness or therebelow;
compact size of the apparatus;
low tooling costs (e.g., only four ring moulds are required for a glass pattern);
a short glass-pattern; replacement time (typically less than 0,5 h).
This object of the invention is achieved on the basis of the characterizing features set forth in the annexed claims.